The invention relates to an electric parking brake, in particular for a commercial vehicle, comprising at least two compressed-air outlets, an electrically controllable valve arrangement having a bistable valve for controlling a distribution of compressed air to the compressed-air outlets, and a compressed-air inlet which may be connected to a compressed-air supply for supplying the valve arrangement and the compressed-air outlets with compressed air from a compressor and/or a compressed-air reservoir.
Electric parking brakes are known, for example, from DE 10 2008 048 207 B4, wherein a compressor supplies the parking brake with compressed air and wherein a valve arrangement having electrically actuable valves and a relay valve regulates the compressed-air supply for consumer circuits, for example a trailer control valve or a spring-loaded emergency brake, which are connected to compressed-air outlets. The parking brake here has an electrically controllable valve which, in addition to pressures which correspond to a permanent open position or closed position of the valve, can also supply the consumer circuits with a gradual intermediate air pressure, for which the controllable valve is operated in a pulsed manner. The parking brake has, at the compressed-air outlet for the spring-loaded emergency brake, a relay valve to which compressed air from the compressed-air source is supplied on the inlet side and whereof the outlet pressure is controlled by the gradual pressure of the blocking valve applied to a control inlet.
DE 10 2008 007 877 B3 discloses a parking brake device having a spring brake cylinder arranged on the outlet side and trailer control valves arranged on the outlet side. The spring brake cylinder is controlled by a relay valve, wherein the relay valve is controlled by a safety valve which has a pneumatic feedback whereby a select low valve switches the lower of two pressures, which is applied at an outlet or at an inlet of the safety valve, through to a control inlet of the safety valve. The safety valve is supplied with regulated compressed air on the inlet side by way of two solenoid valves and, solely in terms of its construction, is a monostable valve wherein a bistability of the safety valve is achieved by the pneumatic feedback.
It shall be understood below that the parking brake is always viewed from the compressed-air supply to the compressed-air outlets. When reference is made to following components, this always means the components which, in terms of the circuit, are arranged closer to the compressed-air outlets in the lines or in the parking brake. The same applies to the words “inlet side” and “outlet side”, wherein “inlet side” refers to the connection which faces the compressed-air supply and “outlet side” refers to the connection of a component which faces the compressed-air outlets. “On the control side” describes the association of a component with a control connection which may be present. It is furthermore understood that, in relation to a pressure level, the term “gradual” should be seen as being between a maximum reservoir pressure and a minimum ambient pressure. The term valve arrangement here is understood to mean an arrangement comprising all the valves and all the line elements located between the valves.
Currently used parking brakes with bistable valves enable stepped, i.e. gradual, braking only above a certain minimum pressure which is applied at the compressed-air outlets, since the emergency brake is automatically engaged below the minimum pressure, which is approximately 1 bar above ambient pressure. This is attributed to the switching behavior of a bistable valve used. In a parking position, bistable valves block the compressed-air supply to the electronic parking brake, whilst the electronic parking brake is connected to a vent line. This vents the parking brake and the spring mechanisms can apply a brake force. In a driving position, the compressed-air supply to the electric parking brake is connected so that the venting of the electronic parking brake is closed and the electronic parking brake releases or is released.
The object of the invention is to provide an electronic parking brake which has as few switchable valves as possible and which reliably supplies compressed air to the compressed-air outlets.
This object is achieved by an electronic parking brake in accordance with embodiments of the invention.
The invention builds on the generic electric parking brake in that the bistable valve is supplied with compressed air by the compressed-air supply on the inlet side irrespective of the switching status of the valve arrangement. The compressed air is at a pressure which is provided by the compressor and/or the compressed-air reservoir. It is thus possible to guarantee that the electric parking brake can always ensure a braking action of the trailer brake. On the other hand, should it be possible for the inlet pressure of the bistable valve to drop to ambient pressure, this could result in the trailer remaining unbraked during a braking procedure and consequently running into the towing vehicle. In the worst case, the towing vehicle/trailer unit can then jackknife. This risk is entirely eradicated by the invention. In particular, it is thus advantageously possible to realize a parking brake whereof the consumers connected downstream of the bistable valve are also reliably supplied with reservoir pressure in the event of a power failure when the bistable valve is switched to its open position. It is therefore advantageously possible to control a status of the compressed-air outlets, at least during travel, by means of the bistable valve alone, without any influence from components, in particular valves, which are connected upstream. By means of the electronic parking brake according to the invention, it is furthermore possible to implement the actuation of an emergency brake of the commercial vehicle and a test function known as a trailer test function. In this case, the braking action of the emergency brake and the service brake of the trailer can be advantageously gradually adjustable, wherein the test function can be executed without it being necessary to move out of a stable parking position. In the trailer test function, before the commercial vehicle is immobilized the driver tests whether a commercial vehicle/trailer unit can also be parked on an incline, even if only the parking brake of the commercial vehicle, and not a brake of the trailer, is activated. To this end, when the parking brake of the commercial vehicle is engaged, the brake of the trailer is released by supplying compressed air to the control line of a trailer control module. If the towing vehicle/trailer unit does not move, then the unit can be immobilized on the incline.
The parking brake according to the invention can have the feature of connecting the bistable valve directly to the compressed-air supply. The direct significance of this is that no active components, in particular no switchable valves, are arranged in a compressed-air line between the compressed-air supply and the bistable valve. It is thus advantageously achieved that the parking brake does not switch a component, for example a solenoid valve, arranged upstream of the bistable valve as a result of a sudden power failure and thereby inadvertently alter a status of the system as a whole.
The invention can advantageously be developed in such a way that the valve arrangement comprises precisely three electrically controllable valves. This is a very small number of controllable valves for supplying compressed air to two or three compressed-air outlets which can be acted upon by a different pressure in each case. The invention can provide for the three electrically controllable valves to comprise the bistable valve. It can furthermore be intended for the electrically controllable valves to be solenoid valves. It is moreover possible to opt for the special case in which the electrically controllable valves comprise at least one 3/2-way valve. In an advantageous development, the 3/2-way valve is connected to a vent line wherein it vents the following components to ambient pressure in a venting position. Provision can also be made for the electrically controllable valves to comprise a 2/2-way valve. Provision can be made for the electrically controllable valves to be preloaded in one of their switching positions. Provision can be additionally or alternatively made here for an electrically controllable valve to have a motor drive for changing the switching position. The invention can, in particular, be constructed in such a way that the bistable valve has a motor drive.
The invention can advantageously be constructed in such a way that the valve arrangement comprises a pneumatically controllable valve for inverting a reservoir pressure for a trailer control module. Inverting the pressure means that the pressure provided is purely a reservoir pressure instead of an ambient pressure, and vice versa. Provision can also be made for the pneumatically controllable valve to be connected to a vent line. The reservoir pressure itself corresponds to a maximum air pressure provided by the compressed-air supply. The invention can advantageously be constructed in such a way that the pneumatically controllable valve is controlled by at least one of the electrically controllable valves. Provision can furthermore be made for the pneumatically controllable valve to be controlled by the bistable valve. It is moreover possible for a select high valve or a select low valve to be connected upstream of the pneumatically controllable valve. This enables interconnections with the bistable valve to be achieved in simple and favorable manner. Provision can furthermore be made for the pneumatically controllable valve to be a 3/2-way valve, wherein the valve can assume an open switching position and a blocking position and wherein the vent line vents the following parking brake components in the blocking position. Provision can be made for the compressed air applied at the pneumatically controllable valve on the inlet side to come directly from the compressed-air supply. Provision can furthermore be made for the pneumatically controllable valve to vent the following components when the compressed air applied at the control side is higher than the ambient pressure. In particular, provision can be made for the pneumatically controllable valve to vent the following components if the pressure delivered by one of two electrically controllable valves on the control side is higher than the ambient pressure.
Provision is preferably made for the valve arrangement to have an electrically controllable valve pair, which provides a gradual compressed-air supply to the at least two compressed-air outlets. It is therefore advantageously possible to provide any pressure to control the trailer control module and the emergency brake cylinders. Provision can be made for the valve pair to consist of a 3/2-way valve and a 2/2-way valve. In this case, provision can be made in particular for the 3/2-way valve to be connected upstream of the 2/2-way valve. Provision can furthermore be made for the valve pair to be formed by two solenoid valves. The solenoid valves can therefore be advantageously controlled by an electrical control device so that a desired pressure can be advantageously provided at the compressed-air outlets. The invention can be developed in such a way that the valve pair comprises a vent line and enables a compressed-air supply and a venting of the compressed-air outlets.
An advantageous development of the invention can be designed in such a way that one of the at least two compressed-air outlets supplies an emergency-brake connection with compressed air, wherein a relay valve is connected upstream of this compressed-air outlet. Provision can be made for the relay valve to be controlled by the gradual compressed air of the valve pair.
Provision can moreover advantageously be made for at least one pressure sensor for measuring the pressure of the compressed air to be arranged between the valve arrangement and one of the compressed-air outlets. It is thus advantageously possible to provide a pressure signal for an electrical control device to enable a reaction to changes in pressure. In particular, the pressure signal of the compressed-air outlets can be taken into account when controlling the emergency brake cylinders or the trailer control module.
The invention can furthermore provide for at least one pressure sensor for measuring the pressure of the compressed air to be arranged within the valve arrangement. In this case, provision can be made in particular for the pressure sensor to be arranged upstream of the control inlet of the relay valve so that compressed air applied at the relay valve on the control side can deliver feedback relating to the status of the relay valve. However, provision can also be made for a pressure sensor to be arranged in a line section immediately after the bistable valve or immediately after the valve pair. It is thereby readily possible to determine the pressure applied at the compressed-air outlets. Provision can be made in particular for a pressure sensor to be arranged in a line section between the valve arrangement and the compressed-air supply. It would be alternatively or additionally possible to also arrange a pressure sensor at the working outlet of the relay valve.
The invention can be advantageously developed in such a way that the bistable valve has a motor drive, in particular a self-locking motor drive. It is thus possible to advantageously achieve a stable position of the bistable valve, even when the bistable valve is not supplied with current. Provision can be made for the bistable valve to have a slide mechanism which is movably mounted in a valve housing and is controlled by the motor drive, and in which a valve body is movably arranged.
Provision can alternatively be made for the bistable valve to be pneumatically actuable.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.